The invention relates to a semiconductor device for producing electromagnetic radiation having a monocrystalline semiconductor body comprising a first region of a first conductivity type and a second region of the second opposite conductivity type forming with the first region a pn junction which can emit electromagnetic radiation at a sufficiently high current strength in the forward direction, while on the second region a blocking layer of the first conductivity type is provided, which has an interruption at the area of an active region of the device, a contract region of the second conductivity type which adjoins a surface of the body and extends at the area of said interruption from the surface into the second region, and a highly doped contact layer of the second conductivity type which is disposed on the blocking layer, also adjoins the surface and is connected to the contact region, a first electrode being provided on the first region and a second electrode being provided on the contact region and the contact layer.
Such a semiconductor device is known from the Japanese Patent Application (Kokai) JP-A 57-143888 laid open to public inspection and published in Patent Abstracts of Japan, vol. 6, Dec. 2, 1982, No. 243 (E-145) p. 144.
In optical telecommunication, electroluminescent diodes are frequently used. These diodes may be composed of different semiconductor materials, such as binary, ternary and quaternary compounds of elements from the columns III and V of the Periodical System, in accordance with the wavelength of the emitted radiation chosen for the relevant application and other optical and electrical properties.
The generated electromagnetic radiation may then be coherent (lasers) or incoherent. The radiation may emanate either through a major surface ("surface-emitting") or at the edge of the semiconductor body ("edge emitting").
For applications in the field of optical telecommunication, a luminous spot of small dimensions and high brightness is generally desired, for which purpose a high current density must be concentrated on a small active region. For this purposes, different methods may be used. A frequently used method consists in providing a blocking layer of a conductivity type opposite to that of the surrounding semiconductor material, this blocking layer locally having an interruption through which the current can flow, while it is blocked elsewhere by the pn junctions between the blocking layer and the adjoining material.
Thus, in a known type of electroluminescent diode (LED), a blocking layer of the first conductivity type is provided on the said second region of the semiconductor body, after which the area of the interruption in the blocking layer a contact region of the first conductivity type contacts via said interruption the second region. The whole current then flows through said contact region and the active electroluminescent part is limited to practically the dimensions of said interruption.
Such a diode may have a small radiation-emanating surface of high radiation intensity and is very suitable as such to be used in the field of optical telecommunication. However, it has been found in practice that due to the high current density even with a very low electrical resistance of the contact region the voltage drop across the diode is still comparatively high, which results in a higher dissipation, which gives rise not only to higher electrical losses, but also to a more rapid aging of the crystals.
In order to reduce the contact resistance, as described in JP-A 57-143888, further a highly doped contact layer of the second conductivity type is provided on the blocking layer and this contact layer adjoins the contact region. Due to the resulting reduction of the contact resistance, a considerably lower voltage drop across the diode is attained.
This structure operates satisfactorily as long as the dimensions of the crystal are not too large, for example not larger than about 300.times.300 .mu.m.sup.2.
However, with larger dimensions, problems arise at high modulation frequencies (higher than, for example, 100 MHz) due to the capacitance caused by the contact layer. In optical telecommunication, higher frequencies are often employed, for which these LED's do not operate sufficiently rapidly.